1. Field of the Invention
The invention is directed to the field of terminating high voltage electrical cables and providing suspension insulators for bare high voltage distribution electrical cables and more particularly to providing electrical stress control for such cables.
2. Description of the Prior Art
The concept of using series connected capacitors to uniformly control electrical stress on a cable termination is well known and some patents found describe their approach as modular because they employ a stacked group of similar components or subassemblies.
U.S. Pat. No. 2,794,063 issued May 28, 1957, to J. H. Nicholas, uses a series of modules each having a flange 42 which is the dielectric for the plates which are the metal coating 46 and 46' on the faces of flanges 42. The capacitance of each module depends upon the thickness of flange 42. Individual modules are connected by garter springs 56.
U.S. Pat. No. 3,197,551 issued Jul. 27, 1965 to S. O. Linderholm, uses a voltage divider of the condenser type for distributing electrical stress. The voltage divider consists of a series of annular capacitor elements 23 to 34 stacked within the insulator housing 13. Each of the capacitor elements 23 to 34 comprises interleaved layers of metallic foil 36 and 37 separated by insulating layers 38, all wrapped around an insulating tube.
Mashikian et al, U.S. Pat. No. 3,479,443 issued Nov. 18, 1969, uses an annular insulator body 18 having tightly packed therein a multiplicity of flat alternately conducting 20 and insulating rings 22. A stress cone 30 connects the metal ring at one end to the conducting sheath 12 on the cable and a metal cap 44 connects the conducting rings 20 to the bared conductor 10.
Rein, U.S. Pat. No. 3,538,241 issued Nov. 3, 1970 uses spaced electrode layers or strips 11 on tape 10 placed on insulated carrier tube 8 to form series connected capacitors connected at one end to conductor 1.
Mashikian et al, U.S. Pat. No. 3,673,305 issued Jun. 27, 1972, surrounds flexible insulating sleeve 38 with a number of modules, each comprising series connected capacitors formed by conducting rings 40 separated by electrically insulating rings 42 formed of a material having a high dielectric constant.
U.S. Pat. No. 3,793,477 issued Feb. 19, 1974 to Wagenaar describes an electrical bushing having condenser elements formed of two or more conducting layers. A gap between conducting layers of one condenser element is completely surrounded by one of the conducting layers of the next adjacent condenser element or the gaps in condenser elements located on the same side of the displaced gap condenser elements are substantially aligned with each other. With either arrangement the points of equal potential stress are substantially uniform. Also see U.S. Pat. No. 4,227,035 issued Oct. 7, 1980 to Wagenaar, et al.
U.S. Pat. No. 4,179,582 issued Dec. 18, 1979 to Garcia includes internal and external grading capacitor stacks which form a closed dielectric filled chamber to provide a uniform voltage distribution between the various interfaces.